PROJECT SUMMARY/ABSTRACT This proposal requests funds to acquire a Zeiss GeminiSEM 300 field emission-scanning electron microscope (FE-SEM) to be housed in the Department of Biomaterials of the Histology and Correlative Microscopy Core (HCMC) facility of New York University College of Dentistry (NYUCD). The HCMC is dedicated to the highest quality research on skeletal tissues and dental materials. The Core provides its users expertise in undecalcified tissue and synthetic specimen preparation as well as imaging support for NYUCD bone, tooth, and oral health research programs. The FE-SEM will replace an aging Zeiss EVO 50 SEM currently housed in the HCMC that will no longer be covered under service contract as per Zeiss (see letter of support). The modestly configured GeminiSEM 300 FE-SEM is $600,000 following a trade-in discount of over $151K for the aging EVO SEM. Although conventional SEM has become a staple of our research, our Major Users express increasing need for structural and compositional characterization with greater spatial resolution and brightness offered by FE-SEM. Current research demands lower acceleration voltages coupled with higher resolution, which is difficult to achieve by conventional SEM. Most of our materials are non-conducting, thus variable pressure (VP) capability will eliminate the need for conductive coating without sacrificing image quality. Biomineralization processes vital to health (e.g. of bones and teeth), often produce different crystal phases, and characterization at the nanoscale is essential for understanding structure-property relationships in design of artificial structures. The GeminiSEM 300 is a VP FE-SEM with accelerating voltages ranging from 0.2 kV to 30 kV, beam current ranging from 3 pA to 20 nA, and nominal resolution ranging from 0.8 nm at 15 kV to 1.4 nm at 1 kV, which provides good resolution even at the low voltages. The instrument has both an annular in-lens secondary electron (SE) and an annular in-lens energy selective ?low loss? backscattered electron detector (BSE). These detectors may be operated at up to 150 Pa pressure in so-called ?NanoVP? mode for topographic and material properties signals respectively. At up to 500 Pa pressure, topographic as well as density-dependent compositional imaging is afforded respectively by a VP SE detector and a pneumatic retractable solid state angle-selective BSE detector. A standard Everhart-Thornley detector allows high vacuum SE imaging. Dr. Timothy G. Bromage is Director of the HCMC with 35 years of electron microscopy experience. He will administer the grant, train users, maintain the instrument, and implement its usage on NYUCD?s ?iLabs? facilities management system. Health research by our NIH-funded users includes bio-integration of implants, bone regeneration around severe defects, inflammation in hard tissue repair, calcium in regulating enamel development, and fracture- and wear-resistant restorative materials with desirable aesthetics. Replacement of the current EVO SEM with the Gemini VP FE-SEM will provide a major step forward, not only in the overall quality of images, but also in the possibility of visualizing details that were not visible with conventional SEM.